I suspect the world would be better if that percentage were even greater.
The Baofeng BF-888S as an SSTV beacon?
Yesterday’s musings about SSTV using the Raspberry Pi has me thinking about creating a little SSTV beacon using the super-inexpensive (less than twenty dollars with charger) BF-888S HT from Baofeng. It’s hard to imagine a cheaper HT than this: it doesn’t even have a display. It has 16 channels, and announces which channel you are on with an (English or Chinese) voice. I used the open-source and free program CHIRP to program this with a set of useful frequencies in the FRS and amateur bands, and it seems to work pretty well.
But could I use it to make an SSTV beacon on UHF?
Seems pretty straightforward. I would just need a little bit of interface between the Pi and the BF-888S. Luckily, the Baofeng does seem to support VOX mode, so in principle just using a little 3.5mm jack should work just fine, but I think I’ll go to the trouble of adding an isolation transformer, a potentiometer to set the levels (probably just a little trim pot) and an AC blocking cap. In theory then I’d just need to play the wav file out, the VOX would pick up the sound and start transmitting. Voila!
One small bummer: the BF-888S does not have an external power jack. If you were going to install this in a permanent location, you’d probably have to rig up a 3.7v power supply to feed in through the battery terminals. Perhaps a good opportunity to 3D print something!
To make a fully functioning beacon, I think you just need to combine the “raspistill” program which can do frame grabs and save them as JPEGS with my “robot36” code which will convert them to wave files, and glue them together with some Python code. A rough prototype could probably be hacked together in an hour. Seems like fun!
Stay tuned.
Addendum: Here’s a link to the BF-888S on Amazon. $17.69! If you add a remote mic and the programming cable, it’ll set you back $31.34. You can find an attempt a the manual here. Many functions are enabled/disabled by holding down the MONI and PTT buttons while turning it on. For instance, tuning to channels 1-5 and doing so sets the VOX on or OFF (and sets the sensitivity, I think, more experimentation to come.)
Comments
Comment from Mark VandeWettering
Time 3/8/2014 at 4:08 pm
I haven’t found the proper PTT schematic (I suspect it’s similar to a Kenwood or the like) but sure, it could be done. Currently I’m just piping the output of the Pi sound card directly into the BF-888S mic jack with a 3.5mm patch cable. It’s easy to overdrive, so you need to be a bit careful on the volume levels to avoid clipping, but other than that, it works just fine. The best reason to use a PTT line is that it won’t accidently trigger if your PC makes a beep sound, but this isn’t a huge problem for the Pi, which isn’t even running a UI.
Comment from Jim Clark
Time 8/19/2014 at 2:03 pm
Very interesting stuff. I am glad to find I am not the only person wondering what these little radios could do with a little tweaking. From the Kenwood connector diagrams I have seen, the typical microphone connection is open unless the PTT switch on the remote mic is pressed. If that is true, then you may have to re-configure the wiring slightly to get VOX working. I am waiting on some 2.5mm stereo plugs for my experiments.
Comment from Joel R
Time 3/7/2014 at 5:56 pm
This is an interesting idea. I’ve been following your SSTV projects closely. You say you are going to use VOX, but I wonder if it has a external mic jack it should have a PTT switch capability. I would think you could wire up the Pi as an “external mic” via those ports. You could trigger the PTT with GPIO and then output the audio via mic-in. I’ve got a older Chinese HT (not this brand/model) as well and I know it had a schematic documenting the ext mic port(s) because I hacked together a programming cable for it.